The yeast Candida albicans is the most important fungal pathogen of humans and can infect virtually any body site, highlighting a remarkable adaptability that allows it to thrive in widely disparate conditions. Mortality is higher than in comparable bacterial infections, partly due to serious deficiencies in diagnostic and treatment options. The projects outlined here derive from a comprehensive genomic analysis of the response of C. albicans to phagocytosis by macrophages, a key antifungal cell type, in which a massive metabolic reorganization accompanies a well-studied morphogenetic program. We have focused on the metabolic changes, which are centered on the key intermediate acetyl-CoA and have shown that mutations in several genes important in the production, consumption or transport of this compound reduce virulence in a mouse model of disseminated candidiasis. Together these studies have shown that C. albicans finds and uses non-preferred carbon sources during infection. Consistent with its unique ecological niche as a mammalian commensal, the regulatory networks that govern the metabolic pathways necessary to assimilate such compounds are significantly different than those in the related, but non-pathogenic, yeast Saccharomyces cerevisiae. Further, we have evidence that these metabolic changes also directly affect processes conventionally thought to be more central to virulence, such as filamentation and pH regulation. In particular, we find that C. albicans can actively change extracellular pH to a dramatic degree (up to 3 units) and hypothesize that that this occurs within the mammalian phagolysosome as a protective measure. We propose here studies to understand acetyl-CoA homeostasis as it relates to virulence, pH modulation, and morphogenesis and outline experiments to decipher how C. albicans has adapted the regulation of alternative carbon utilization to meet its in vivo needs. Lay Summary: Fungal infections kill -10,000 people (and rising) per year in the U.S., making further studies directed towards eventual drug development imperative. This proposal uses an isolated immune system- fungal model system using Candida albicans, the most important fungal pathogen, to study basic cellular metabolism, changes in which are suggested to be a key component of the infection process.